APPLICANT'S ABSTRACT: Chronic alcohol consumption is considered a major pathogenic factor in the development of hepatocellular carcinoma (HCC). However, the presence of other factors in the alcoholic patient, most notably hepatitis, smoking and/or poor diet, make it difficult to determine the precise mechanisms whereby alcohol affects the development and/or progression of HCC. Previous reports from our laboratory demonstrate increased expression and function of inhibitory guanine nucleotide proteins (Gi-proteins) in more than 80% of human HCC specimens when compared to normal, pair matched liver specimens. Furthermore stimulation of Gi- proteins in HCC increases cell mitogenesis via a mitogen activated protein kinase (MAPK) cascade in HCC, an effect not observed in normal hepatocytes. Following chronic exposure to ethanol we have recently reported selective up regulation of Gi-protein dependent mitogenesis in HCC versus normal, non-neoplastic hepatocytes Based on these observations and current literature, our central hypothesis is that " The increased cellular mitogenesis characteristic of HCC is dependent, at least in part, on Gi-protein regulation of MAPK activity. Furthermore, we hypothesize that "chronic exposure to ethanol acts to selectively up regulate these pathways in HCC as compared to normal hepatocytes and, in doing so, accelerates tumor growth." This NIAAA exploratory/developmental grant will determine the effects of ethanol on changes in expression and function of specific components of Gi-protein-MAPK dependent signaling cascades in HCC. Using in vitro human and animal models of HCC in conjunction with normal quiescent and proliferating hepatocytes, we will define: (i) the roles of specific components of Gi-protein-MAPK signaling in regulating cell proliferation in normal and transformed (HCC) hepatocytes, and (ii) the dose and temporal effects of ethanol and ethanol metabolites on the expression and function of Gi- protein-MAPK signaling pathways in normal and transformed hepatocytes. We anticipate these studies will provide a critical insight into the understanding of how ethanol regulates a signal transduction/growth regulatory pathway essential to normal and transformed cell function and mitogenesis. We believe this level of understanding of the etiology of HCC at the cellular level is critical to the future development of in vivo studies that allow a clearer, clinical understanding of HCC, as well as the potential for developing alternative treatments for therapeutic intervention in this lethal malignancy.